Piezoelectric substrate and surface acoustic wave filter using the same

ABSTRACT

Disclosed are a piezoelectric substrate and a surface acoustic wave (SAW) filter. A piezoelectric substrate  10 a includes a base member  11  including an oxide layer  12  with a plurality of grooves  12 a on one surface of the base member  11 ; a buffer member  13  being formed on the oxide layer  12  to expose one end and another end of the oxide layer  12 ; an insulating member  14  being formed on another surface of the base member  11 ; and a piezoelectric member  15  being formed on the buffer member  13 . A SAW filter using the piezoelectric substrate  10 a, includes the base member  11  including the oxide layer  12  with the plurality of grooves  12 a on one surface; the buffer member  13 ; the insulating member  14 ; the piezoelectric member  15 ; and a plurality of interdigital transducer (IDT) electrodes  17  and  17  being formed on the piezoelectric member  15  to receive an electrical signal, filter the electrical signal, and output the filtered electrical signal.

BACKGROUND

1. Field

The present invention relates to a piezoelectric substrate and a surfaceacoustic wave (SAW) filter, and more particularly, to a piezoelectricsubstrate and a SAW filter that can improve thermal transmission andremove bi-directional loss by surface wave reflection by a plurality ofgrooves.

2. Background

A surface acoustic wave (SAW) filter is used as a frequency filter thatcan generate and distribute elastic surface waves by a voltage when thevoltage is supplied and thereby can filter the elastic surface waves.The SAW filter includes various types such as a plurality of normalstate interdigital transducer (IDT) electrodes and weighted IDTelectrodes. In the case of the normal state IDT electrodes, the overlapsize between the electrodes is constant. On the other hand, in the caseof the weighted IDT electrodes, the pitch and the overlap size betweenthe electrodes changes.

FIG. 1 is a perspective view of a conventional SAW filter. As shown inFIG. 1, the conventional SAW filter includes a piezoelectric substrate1, a plurality of IDT electrodes 2 and 3, and a plurality of reflectors4 and 5. Hereinafter, each component will be described.

The piezoelectric substrate 1 used for the SAW filter is formed bymanufacturing lithium niobium oxide (LiNbO₃), lithium tantalum oxide(LiTaO₃), quartz, and the like in ingot and then subsequently cuttingthe ingot using a crystal growth scheme. In the case of thepiezoelectric substrate applied with the crystal growth scheme, thepiezoelectric substrate may have an excellent electrical characteristic.However, when manufacturing such piezoelectric substrate, expensiveequipments may be needed and thus manufacturing costs may increase. Inorder to solve the above problems, the piezoelectric substrate 1 shownin FIG. 1 is applied.

The piezoelectric substrate 1 consists of a wafer 1 a made of silicon(Si) or diamond, a piezoelectric member 1 b, and a buffer member 1 c.

The plurality of IDT electrodes 2 and 3, and the plurality of reflectors4 and 5 are formed on the piezoelectric member 1 b. The piezoelectricmember 1 b is formed on the wafer 1 a made of Si or diamond. Thepiezoelectric member 1 b may use alumina (Al₂O₃), AnO, AlN, barium titanoxide (BaTiO₃), or PZT series of piezoelectric ceramic and apiezoelectric material with greater piezoelectric coefficient. Whendisposing the piezoelectric member 1 b on the wafer 1 a made of Si ordiamond, the piezoelectric performance may be deteriorated due to asurface phenomenon. Also, when forming the piezoelectric member 1 b onthe wafer 1 a made of Si, the piezoelectric member 1 b is formed in acrystal direction and thus a process condition becomes difficult. Inorder to solve the above problem, the buffer member 1 c is interposedbetween the wafer 1 a and the piezoelectric member 1 b. The buffermember 1 c uses any one of silicon oxide (SiO2), alumina (Al₂O₃), andoxide tantalum (Ta₂O₅) to thereby remove the surface phenomenon whenforming the piezoelectric member 1 b on the wafer 1 a and improve thedeterioration of the piezoelectric performance or the process condition.

The plurality of IDT electrodes 2 and 3 includes the input IDT electrode2 and the output IDT electrode 3 to which input/output electrodes T1 andT2 are connected respectively. A pattern of the plurality of IDTelectrodes 2 and 3 is formed by photo etching after forming a conductivematerial on the piezoelectric substrate 1.

The plurality of reflectors 4 and 5 is formed on the piezoelectricsubstrate 1 so that the surface elastic wave energy generated from theplurality of IDT electrodes 2 and 3 may be located at an outside of theplurality of IDT electrodes 2 and 3 according to a resonant condition.Through this, it is possible to minimize the surface wave reflection andthereby remove the bidirectional loss. As shown in FIG. 1, the pluralityof reflectors 4 and 5 forms a metal film in grating. In addition to thereflectors 4 and 5, an absorber (not shown) is provided to form grooves(not shown) on the piezoelectric substrate 1. When a piezoelectricsubstrate of a conventional surface acoustic wave (SAW) filter forms abuffer member between a wafer made of silicon (Si) or diamond and apiezoelectric member to thereby improve a surface phenomenon, a seriousproblem may occur in the crystal structure. Specifically, in comparisonto a single crystal, since a thin film is formed, durability power maybe decreased. Also, since an absorber including a groove or a reflectorin grating structure of a metal thin film on a piezoelectric substrateis formed, it is difficult to reduce the size of the SAW filter.

The present invention is conceived to solve the above described problemsand thus provides a piezoelectric substrate that can form an oxide layerwith a plurality of grooves on a base member, selectively form a buffermember and a piezoelectric member on the oxide member and thereby canimprove thermal transmission by the plurality of grooves and also can bereadily manufactured, and a manufacturing method of the same.

The present invention also provides a SAW filter that can form an oxidelayer with a plurality of grooves on a base member, selectively form abuffer member and a piezoelectric member on the oxide layer, and therebycan remove bidirectional loss by the surface wave reflection of theplurality of grooves formed on a piezoelectric substrate and thus canreduce the size, and a manufacturing method of the same.

According to an aspect of the present invention, there is provided apiezoelectric substrate including: a base member including an oxidelayer with a plurality of grooves on one surface of the base member; abuffer member being formed on the oxide layer to expose one end andanother end of the oxide layer; an insulating member being formed onanother surface of the base member; and a piezoelectric member beingformed on the buffer member.

According to another aspect of the present invention, there is provideda method of manufacturing a piezoelectric substrate, including: formingan oxide layer with a plurality of grooves on one surface of a basemember by anodizing; selectively applying a buffer material on the oxidelayer to expose one end and another end of the oxide layer to form abuffer member; applying an insulating material on another surface of thebase member to form an insulating member; and applying a piezoelectricmaterial on the buffer member to form a piezoelectric member.

According to still another aspect of the present invention, there isprovided a surface acoustic wave (SAW) filter including: a base memberincluding an oxide layer with a plurality of grooves on one surface; abuffer member being formed on the oxide layer to expose one end andanother end of the oxide layer; an insulating member being formed onanother surface of the base member; a piezoelectric member being formedon the buffer member; and a plurality of interdigital transducer (IDT)electrodes being formed on the piezoelectric member to receive anelectrical signal, filter the electrical signal, and output the filteredelectrical signal.

According to yet another aspect of the present invention, there isprovided a method of manufacturing a SAW filter, including: forming anoxide layer with a plurality of grooves on one surface of a base memberby anodizing; selectively applying a buffer material on the oxide layerto expose one end and another end of the oxide layer to form a buffermember; applying an insulating material on another surface of the basemember to form an insulating member; applying a piezoelectric materialon the buffer member to form a piezoelectric member; and applying aconductive material on the piezoelectric member to form a plurality ofIDT electrodes by photo etching.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be described in detail with reference to thefollowing drawings in which like reference numerals refer to likeelements wherein:

FIG. 1 is a perspective view of a conventional surface acoustic wave(SAW) filter;

FIG. 2 is a perspective view of a piezoelectric filter according to thepresent invention;

FIG. 3 is a perspective view of a base member shown in FIG. 2;

FIG. 4 is a perspective view of a SAW filter using a piezoelectricsubstrate according to the present invention;

FIG. 5 illustrates a manufacturing process of a piezoelectric substrateand a SAW filter according to the present invention; and

FIG. 6 is a side cross-sectional view illustrating another embodiment ofa base member shown in FIG. 5.

DETAILED DESCRIPTION

Hereinafter, embodiments of a piezoelectric substrate according to thepresent invention will be described with reference to the accompanyingdrawings.

FIG. 2 is a perspective view of a piezoelectric filter 10 a according tothe present invention, and FIG. 3 is a perspective view of a base member11 shown in FIG. 2. As shown in FIGS. 2 and 3, the piezoelectricsubstrate 10 a includes the base member 11, an oxide layer 12, a buffermember 13, an insulating member 14, and a piezoelectric member 15.

As shown in FIGS. 2 and 3, the base member 11 includes the oxide layer12 that is formed with a plurality of grooves 12 a on one surface. Theplurality of grooves 12 a formed on the oxide layer 12 a is formed tohave a nano-pore array structure by anodizing, as shown in FIG. 3. Sincethe plurality of grooves 12 a formed on the oxide layer 12 has thenano-pore array structure, it is possible to increase the surface areaand thereby improve thermal transmission. Therefore, it is possible toreadily discharge heat generated from a SAW filter 10 of FIG. 4 to anoutside. The plurality of grooves 12 a formed to more readily dischargethe heat generated from the SAW filter 10 to the outside may be formedon one surface of the base member 11 as shown in FIG. 3, or may beformed on both surfaces of the base member 11 as shown in FIG. 6.

The base member 11 formed with the oxide layer 11 may use aluminum (Al),niobium (Nb), tantalum (Ta), zirconium (Zr), titanium (Ti), copper (Cu),carbon monoxide (NbO), and zinc (Zn), or at least two different alloysthereof, or all general metals. Specifically, a metal member such asaluminum (Al), niobium (Nb), tantalum (Ta), zirconium (Zr), titanium(Ti), copper (Cu), and zinc (Zn) may be individually selected and thenbe applied. Also, alloys of aluminum (Al) and niobium (Nb), or alloys ofaluminum (Al), niobium (Nb), and tantalum (Ta) may be applied. Such thebase member 11 may adopt a solid member such as carbon monoxide (NbO).

The oxide layer 12 formed on the base member 11 may use any one ofalumina (Al₂O₃), oxide niobium (Nb₂O₅), oxide tantalum (Ta₂O₅), oxidezirconium (ZrO₂), oxide titanium (TiO₂), oxide copper (CuO), and oxidezinc (ZnO) depending on a material of the base member 11.

The buffer member 13 may be formed on the oxide layer 12 to expose oneend and another end of the oxide layer 12 as a buffer layer for removingthe surface effect. The surface effect may occur when directly formingthe piezoelectric member 15 on the base member 11. Specifically, asshown in FIG. 2, the buffer member 13 is selectively formed to fill inthe plurality of grooves 12 a that is formed on a central portion of theoxide layer 12 whereby the plurality of grooves 12 a formed on one endand another end of the oxide layer 1 is externally exposed. The buffermember 13 may adopt the same material as the oxide layer 12 so that thebuffer member 13 may readily fill in the plurality of grooves 12 aformed on the central portion of the oxide layer 12. Specifically,depending on the material of the oxide layer 12, the buffer member 13may use any one of alumina (Al₂O₃), oxide niobium (Nb₂O₅), oxidetantalum (Ta₂O₅), oxide zirconium (ZrO₂), oxide titanium (TiO₂), oxidecopper (CuO), and oxide zinc (ZnO).

The insulating member 14 is formed on another surface of the base member11 in order to prevent the base member 11 from contacting with theexternal conductive material and being electrically short. Even when theoxide layer 12 with the plurality of grooves 12 a is formed on anothersurface of the base member 11 as shown in FIG. 3, the insulating member14 may adopt the same material as the buffer member 13 and readily fillin the grooves 12 a. Specifically, depending on the material of thebuffer member 13 using the same material as the oxide layer 12, theinsulating member 13 may use any one of alumina (Al₂O₃), oxide niobium(Nb₂O₅), oxide tantalum (Ta₂O₅), oxide zirconium (ZrO₂), oxide titanium(TiO₂), oxide copper (CuO), and oxide zinc (ZnO).

Since the piezoelectric member 15 is formed using the buffer member 13as a medium, it is possible to more easily manufacture the piezoelectricmember 15. The piezoelectric member 15 may use oxide zinc (ZnO),aluminum nitride (AlN), barium titanium oxide (BaTiO₃), andpiezoelectric series of piezoelectric ceramic, and a piezoelectricmaterial with greater piezoelectric coefficient.

As described above, since the buffer member 13, the piezoelectric member15, and a plurality of interdigal transducer (IDT) electrodes 16 and 17are selectively formed on the oxide layer 12, thermal transmission maybe increased by the plurality of grooves 12 a formed on the oxide layer12. Therefore, it is possible to enable high power when manufacturingthe SAW filter 10 of FIG. 4 using the piezoelectric substrate 10 a.

Hereinafter, a manufacturing of the piezoelectric substrate 10 aconstructed as above will be described with reference to theaccompanying drawings.

When the base member 11 is provided as shown in a part (A) of FIG. 5,the oxide layer 12 with the plurality of grooves 12 a may be formed onone surface of the base member 11 by anodizing as shown in a part (B) ofFIG. 5. The plurality of grooves formed on the oxide layer 12 has anano-pore array structure. In order to improve thermal transmission, theoxide layer 12 may be formed to have the plurality of grooves on bothsurfaces of the base member 11. The oxide layer 12 with the plurality ofgrooves 12 a may apply anodizing to the base member 11. The anodizingdenotes technology that can apply a positive electrode to the basemember 11 and apply a negative electrode to the solution and thereby cantreat the surface. The anodizing may form the oxide layer 12 on the basemember 11 by oxygen generating from the positive electrode to therebyform a film.

In order to form the oxide layer 12 using anodizing, the base member 11may be formed by using any one of aluminum (Al), niobium (Nb), tantalum(Ta), zirconium (Zr), titanium (Ti), copper (Cu), carbon monoxide (NbO),and zinc (Zn).

When the oxide layer 12 is formed on the base member 11, the buffermember 13 may be formed by selectively applying a buffer material on theoxide layer 12 to expose one end and another end of the oxide layer 12as shown in a part (C) of FIG. 5. The buffer member 13 may be formed bymasking a photosensitive film on remaining portions excluding a desiredportion, i.e. on one end and another end of the oxide layer 12 using aphoto process and then applying the buffer material thereon. The buffermember 13 as shown in the part (C) of FIG. 5 may be formed by removingthe photosensitive film. When forming the buffer member 13, unevennessmay significantly occur on the buffer member 13 as shown in the part (C)of FIG. 5. In this case, it is possible to polish the surface of thebuffer member 13 using chemical mechanical polishing (CMP).

When the buffer member 13 is selectively formed on the oxide layer 12,the insulating member 14 may be formed by applying an insulatingmaterial on another surface of the base member 11 as shown in the part(C) of FIG. 5. When simultaneously or separately manufacturing thebuffer member 13 and the insulating member 14, the insulating member 14may be formed prior to forming of the buffer member 13. When the oxidelayer 12 with the plurality of grooves 12 a is formed on another surfaceof the base member 11 as shown in FIG. 6, the insulating member 14 maybe formed to fill in the plurality of grooves 12 a. When the insulatingmember 14 is formed to fill in the plurality of grooves 12 a, polishingmay be performed using CMP as necessary.

For simultaneous or separate manufacturing, the same material may beapplied to the buffer material of the buffer member 13 and theinsulating material of the insulating member 14. Specifically, each ofthe buffer material of the buffer member 13 and the insulating materialof the insulating member 14 may use any one of alumina (Al₂O₃), oxideniobium (Nb₂O₅), oxide tantalum (Ta₂O₅), oxide zirconium (ZrO₂), oxidetitanium (TiO₂) oxide copper (CuO), and oxide zinc (ZnO). The buffermember 13 and the insulating member 14 using such materials may beformed by any one of silk printing, dispensing, deposition, sputtering,CVD, air nozzle spraying, electrode plating, and electroless plating.

Air nozzle spraying may form any one of alumina (Al₂O₃), oxide niobium(Nb₂O₅), oxide tantalum (Ta₂O₅), oxide zirconium (ZrO₂), oxide titanium(TiO₂), oxide copper (CuO), and oxide zinc (ZnO) to oxide-based nanopowders with the size of 10 nm through 100 nm and then quickly apply thenano powders. Since air nozzle spraying is applied, it is possible toreadily fill the buffer member 13 or the insulating member 14 in theplurality of grooves 12 a formed on the oxide layer 12.

When the buffer member 13 or the insulating member 14 is formed, thepiezoelectric member 15 may be formed by applying a piezoelectricmaterial on the buffer member 13. The piezoelectric member 15 may beformed on the buffer member 13 by using any one of silk printing,dispensing, deposition, sputtering, CVD, and air nozzle spraying.

The insulating member 14 and the piezoelectric member 15 may bemanufactured by masking one end and another end of the oxide layer 12using a photo process, so that the insulating member 14 and thepiezoelectric member 15 may not be formed in the plurality of grooves 12a that is formed on one end and another end of the oxide layer 12.

Hereinafter, an embodiment of the SAW filter 10 using the piezoelectricsubstrate 10 will be described with reference to the accompanyingdrawings.

FIG. 4 is a perspective view of the SAW filter 10. The SAW filter 10includes a base member 11, an oxide layer 12, a buffer member 13, aninsulating member 14, a piezoelectric member 15, and a plurality of IDTelectrodes 16 and 17.

The base member 11, the oxide layer 12, the buffer member 13, theinsulating member 14, and the piezoelectric member 15 of FIG. 4constituting the SAW filter 10 have the same configuration and functionof the base member 11, the oxide layer 12, the buffer member 13, theinsulating member 14, and the piezoelectric member 15 of FIG. 2 and thusfurther detailed descriptions will be omitted here. Hereinafter, theplurality of IDT electrodes 16 and 17 will be described.

The plurality of IDT electrodes 16 and 17 may be formed on thepiezoelectric member 15 to receive electrical signals, filter the same,and output the filtered electrical signals. Specifically, whenelectrical signals are received by a terminal Ti connecting with one ofthe plurality of IDT electrodes, for example, the IDT electrode 16, thepiezoelectric member 15 may convert the electrical signals to mechanicalsignals and then filter the same by a pattern of the plurality of IDTelectrodes 16 and 17. The filtered mechanical signals may be againtransformed to electrical signals and be output via another terminal T2connecting with remaining IDT electrode, for example, the IDT electrode17.

When applying a greater electrical signal to the plurality of IDTelectrodes 16 and 17, heat may be readily discharged via the pluralityof grooves 12 a formed on the buffer member 13 and the oxide layer 12,enabling the high power of the SAW filter 10. When the SAW filter 10 isapplied to the high frequency and thereby the pattern of the pluralityof IDT electrodes 16 and 17 is constructed as a narrow pitch, thethermal discharge may be simplified, preventing the short from occurringbetween patterns of the plurality of IDT electrodes 16 and 17 to improvedurability.

As described above, the plurality of grooves 12 a formed on one end andanother end of the oxide layer 12 may be externally exposed byselectively forming the buffer member 13, the piezoelectric member 15,and the plurality of IDT electrodes 16 and 17 on the oxide layer 12.Therefore, it is possible to remove the bidirectional loss.Specifically, since the buffer member 13 formed on the oxide layer 12fills in the plurality of grooves 12 a, it is possible to remove thebidirectional loss by reflection due to a medium difference between aportion where the buffer member 13 is formed on the oxide layer 12 andone and another ends of the where the buffer member 13 is not formed.Therefore, the SAW filter 10 does not need to additionally form thereflectors 4 and 5 of FIG. 1 and thus it is possible to reduce the sizeof the SAW filter 10.

Hereinafter, a manufacturing method of the SAW filter 10 using thepiezoelectric substrate 10 a, constructed as above, will be describedwith reference to the accompanying drawings.

When the piezoelectric substrate 10 a is manufactured as shown in parts(A) through (D) of FIG. 5, the SAW filter 10 may be manufactured usingthe piezoelectric substrate 10 a. Specifically, when the piezoelectricmember 15 is formed through the manufacturing process of thepiezoelectric substrate 10 a as shown in the part (D) of FIG. 5, theplurality of IDT electrodes 16 and 17 may be formed by a photo etchingprocess after applying conductive material on the piezoelectric member15 as shown in a part (E) of FIG. 5. The conductive material for formingthe plurality of IDT electrodes 16 and 17 may be any one of aluminum(Al), niobium (Nb), tantalum (Ta), zirconium (Zr), titanium (Ti), copper(Cu), carbon monoxide (NbO), and zinc (Zn). The conductive material maybe applied to the piezoelectric member 15 after masking one end andanother end of the oxide layer 12 using a photo process, so that theconductive material may not be applied to the plurality of grooves 12 aformed on one end and other end of the oxide layer 12.

When the conductive material is applied to the piezoelectric member 15,the applied conductive material may be masked and then the plurality ofIDT electrodes 16 and 17 may be formed by using an etching process. Theetching process may apply dry etching using a reactive ion etcher sothat etching may simultaneously occur in horizontal and verticaldirections.

According to the present invention, there is provided a piezoelectricsubstrate and a surface acoustic wave (SAW) filter that can improvethermal transmission by a plurality of grooves formed on a piezoelectricsubstrate and thus can enable high power when manufacturing a SAW filterand also can remove directional loss by the surface wave reflectionusing the plurality of grooves and thus can reduce the size of the SAWfilter.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to effect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, various variations and modificationsare possible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

1. A method of manufacturing a piezoelectric substrate, comprising: forming an oxide layer with a plurality of grooves on one surface of a base member by anodizing; selectively applying a buffer material on the oxide layer to expose one end and another end of the oxide layer to form a buffer member; applying an insulating material on another surface of the base member to form an insulating member; and applying a piezoelectric material on the buffer member to form a piezoelectric member.
 2. The method of claim 1, wherein, in the forming of the oxide layer, the plurality of grooves formed on the oxide layer is formed to have a nano-pore array structure.
 3. The method of claim 1, wherein the forming of the oxide layer forms the oxide layer with the plurality of grooves on both surfaces of the base member by anodizing.
 4. The method of claim 1, wherein in the forming of the buffer member and the forming of the insulating member, each of a buffer material and an insulating material uses any one of alumina (Al₂O₃), oxide niobium (Nb₂O₅), oxide tantalum (_(Ta) ₂O₅), oxide zirconium (ZrO₂), oxide titanium (TiO₂), oxide copper (CuO), and oxide zinc (ZnO).
 5. The method of claim 1, wherein the forming of the buffer member further comprises polishing the surface of the buffer member using a chemical mechanical polishing (CMP) process.
 6. The method of claim 1, wherein in the forming of the buffer member and the forming of the insulating member, each of the buffer material and the insulating material is applied by using any one of silk printing, sputtering, CVD, air nozzle spraying, electrode plating, and electroless plating.
 7. The method of claim 1, wherein in the forming of the piezoelectric member, the piezoelectric material is applied by using any one of silk printing, sputtering, CVD, and air nozzle spraying. 